An L-2 spouse may work for any employer, since the authorisation follows from the status itself. What the spouse cannot do is outlast the principal: derivative status ends when the L-1B period does, and specialized-knowledge status has a five-year maximum. A spouse who wants to remain independently needs a classification of her own.
Derivative work authorisation has an expiry date attached to somebody else
Families plan around the permission and forget the term. The right to work arrives immediately and feels permanent, and it is not: it is measured by the principal's status, which in this category runs no more than five years in total. Hypothetical example: two years into an assignment, the spouse of a transferee from Sainte-Cécile-de-Milton is offered a senior role by an American employer who assumes she is free to accept it indefinitely.
She is free to accept it now. Whether she can still hold it in year six depends on either the principal obtaining a different classification or her employer sponsoring her in its own right, and that conversation is far easier at the offer stage than three years later. Children in L-2 may study, and they remain dependants only while unmarried and under twenty-one, so a child's twenty-first birthday belongs on the same timeline.